Methods and systems for distributing broadcast messages on various networks

ABSTRACT

Methods and systems for sending a broadcast message in frequency hopping and other systems. Instead of sending a complete message separately to each device, a relatively small packet or “chirp” is sent. These chirps are either targeted at known devices or sent in a manner to sweep the RF band. Devices that hear the chirps get information about the channel and/or time that the broadcast data will be sent. These devices then listen for the broadcast data as instructed, e.g., at the specified time on the specified channel. A system may alternatively, or in addition, use a scheduled hopping sequence break as a broadcast moment. Such a broadcast moment can be scheduled to periodically interrupt the node hopping sequences so that, at such times, many or all nodes are scheduled to be on the same channel for potential broadcasts.

RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 12/636,128, entitled “Methods and Systems for DistributingBroadcast Messages on Various Networks” and filed on Dec. 11, 2009, nowallowed, which claims the benefit of U.S. Provisional Application Ser.No. 61/247,110, entitled “Methods and Systems For Broadcasting in aFrequency Hopping Network” and filed Sep. 30, 2009, the entire contentsof which are incorporated by this reference.

FIELD

This disclosure relates generally to improved radio communication,including methods and systems used in frequency hopping networks andadvanced metering infrastructure (AMI) systems, among otherenvironments.

BACKGROUND

Radio communication-based networks are widespread and used for a varietyof applications. Such networks are commonly employed in AMI systems thatmeasure, collect, and/or analyze utility usage from electricity, gas,water, and other meters through various communication media. In theseand other networks, some messages may be sent as broadcasts, i.e., sentto two or more recipients simultaneously. Broadcast messages may beintended for ultimate receipt by most or all nodes of the network. In anAMI system, for example broadcast messages may be used to send loadshedding, new rate, and other generally-applicable information.Regardless of the purpose, broadcasting a message typically involves atransmitter sending a message and one or more devices receiving themessage at roughly the same time.

“Broadcasting” a message involves sending a message to two or morepotential recipients simultaneously. Unlike broadcasting on a wire or asingle channel radio frequency (“RF”) system which can be relativelysimple, broadcasting messages on many frequency hopping systems can bedifficult. Since recipient devices can be on different channels at anypoint in time, such devices will not receive the same broadcast message.Since devices in a frequency hopping network can be on differentchannels, such sending needs to be repeated for different devices ondifferent frequencies. In many circumstances, the time required to sendand resend a broadcast type message with acknowledgement is too timeconsuming to be practical. Additional issues complicate broadcasting onfrequency hopping systems. Various regulations may further restrict thebroadcasting options available in frequency hopping networks, forexample, by preventing the uneven use of channels. Additionally, it isgenerally desirable that the addition of any broadcast capabilities thatare added to a system will have minimal impact on regular (i.e.,non-broadcast) transmissions.

SUMMARY OF THE INVENTION

Various techniques for sending a broadcast message quickly andefficiently in frequency hopping and other networks are disclosed.Instead of sending a complete message separately to each device in thenetwork, a relatively small packet or “chirp” is sent. These chirps areeither targeted at known devices or are sent in a manner to sweep theradio frequency (“RF”) band. Devices that hear the chirps will typicallyreceive information about the channel and/or time that the actualbroadcast data will be sent. These recipient devices will then listenfor the broadcast data as instructed, e.g., at the specified point intime on the specified channel.

One exemplary embodiment uses a device with data storage for storing abroadcast message to be distributed to recipient devices. The devicealso has transmission hardware for distributing the broadcast message tothe recipient devices by sending a chirp packet and then the broadcastmessage. The chirp packet indicates to any recipient devices receivingthe chirp packet that the broadcast message will be sent subsequently.For example, the chirp packet may identify a channel on which thebroadcast message will be sent, a time at which the broadcast messagewill be sent, and/or provide information that allows recipient devicesto avoid receiving duplicate broadcast messages. In one embodiment,these devices are part of a frequency hopping network in which nodes ofthe network communicate based on one or more frequency hoppingsequences. The device may send the chirp packet on multiple (andpossibly every) channel used on the frequency hopping network.

Another exemplary embodiment is a method that involves receiving abroadcast message at a first device for distribution to recipientdevices. A chirp packet is then sent to potential recipient devicesindicating that a broadcast message will be sent subsequently. Thebroadcast message is then sent on a channel and time to which the chirppacket recipients will be listening.

Yet another embodiment involves a mesh network having a plurality ofdevices configured to communicate using a frequency hopping sequence. Afirst device of the plurality of devices is configured to store and senda broadcast message and send a chirp packet indicating that thebroadcast message will be sent subsequently. The first device may beconfigured to sweep a frequency hopping sequence with the chirp packet,i.e., to send the chirp packet on each channel of the frequency hoppingsequence. A second device of the plurality of devices is configured toreceive the chirp message, and, in response to chirp message, listen forthe broadcast message on a first channel different from a second channelspecified by the frequency hopping sequence. The first device may havereceived the broadcast message in a variety of ways. In one embodiment,the first device receives the broadcast message by periodicallylistening on a channel not specified by the first device's frequencyhopping sequence. At least some of the plurality of devices may thensend chirp packets indicating to any recipient devices that thebroadcast message will be sent subsequently. Additional techniques andcombinations of techniques for distributing a broadcast message may alsobe used.

These embodiments are mentioned to provide examples and aidunderstanding. Additional embodiments and advantages are also discussedin the Detailed Description and will become readily apparent to thoseskilled in the art. As will be realized, the invention is capable ofother and different embodiments, and its several details are notessential, but rather are capable of modifications in various obviousrespects, all without departing from the invention. Accordingly, thedrawings and description are to be regarded as illustrative in nature,and not as restrictive.

BRIEF DESCRIPTION OF THE FIGURES

The above described and other features, aspects, and advantages of thepresent disclosure are better understood when the following DetailedDescription is read with reference to the accompanying drawings,wherein:

FIG. 1 is a system diagram illustrating an exemplary networkenvironment;

FIG. 2 is a flow diagram showing communication between nodes of anexemplary network;

FIG. 3 is an illustration of exemplary differences in hopping sequencebetween two radios;

FIG. 4 is an illustration of an exemplary chirp packet; and

FIG. 5 is a flow chart illustrating an exemplary method of using a chirppacket to indicate that a broadcast message will be subsequently sent.

DETAILED DESCRIPTION

FIG. 1 is a system diagram illustrating an exemplary networkenvironment. Other embodiments may involve alternative networks andsystems. The network 10 shown in FIG. 1 comprises access points 20, 21and other devices, referred to herein as nodes 30-41. The nodes 30-41work together to create a mesh network in which each node generallycomprises a radio that can speak to and respond to neighboring radiodevices of neighboring nodes. In the case of an AMI system, each suchnode may comprise or connect to an endpoint device such as a utilitymeter or appliance, or may not itself comprise or connect to an endpointdevice. Thus, generally, a node may interact with an endpoint device,act as part of the network, or both, and may do so simultaneously. Theradio of each node may have a programmable logic controller (PLC)-likedevice. Such a device can enable the radio to function like a smallcomputer, carrying out appropriate computing and command functions. Thusintelligence in some or all of the radios may be used to delegate anddistribute commands throughout the network 10. The radio may, but neednot necessarily, allow two-way communication.

As an example of a utility monitoring network, each node of network 10that comprises or connects to an endpoint may collect information aboututility consumption at that endpoint and send such information throughthe network 10 to an access point 20, 21, where it may be collected by autility company, for example, for billing and/or monitoring purposes. Asa more specific example, an endpoint device radio may generate a packetof data that is transmitted to some destination, such as an access pointdestination. The packet may be addressed to the destination and enteredinto the network. The data packet traverses the network by hopping fromradio to radio (node to node) in the direction of thedestination-addressed radio. The route chosen for traversing the networkmay be dynamic and/or may employ routing. Generally, the network 10 willattempt to minimize the number of hops to increase transmission speed.

The radio and/or other components at a node of the network may bebattery-powered, line-powered, or powered by any other suitable powersource and attached via any suitable connection. Nodes will alsogenerally comprise a time-keeping component such as a crystaloscillator.

FIG. 2 is a flow diagram showing exemplary communication between nodes200, 210. The first node 200 comprises a data storage component 201, acrystal oscillator 202, transmission hardware 203 such as a radio, and apower source 204 such as a battery or AC connection. Similarly, thesecond node 210 also comprises a data storage component 211, a crystaloscillator 212, and transmitter 213 such as a radio, and a power source214 such as a battery or AC connection. The first node 200 may receivemessages and send those messages to other nodes, such as the second node210, using the transmission hardware 203, for example, after temporarilystoring, using, and even modifying such messages in the data storagecomponent 201. The first node 200 may also generate new messages, suchas chirp messages, and send such messages to the second node 210 and/orother neighboring nodes. The second node 210 may also be configured toreceive and send messages.

FIG. 3 is an illustration of exemplary differences in hopping sequencesbetween two radios. The radios utilize a multi-channel communicationscheme which is supported by accurate time-keeping at each radio node.At any given point in time, a radio is going through its hoppingsequence. For example, RADIO 1 of FIG. 3 has a hopping sequence offrequencies F₁ 301, F₂ 302, F₃ 303, F₄ 304, F₅ 305, F₆ 306, F₇ 307 andRADIO 2 has a similar sequence of frequencies F₁ 311, F₂ 312, F₃ 313, F₄314, F₅ 315, F₆ 316, F₇ 317. Each block of the hopping sequencerepresents an increment of time or dwell time 310, for example, 700milliseconds, in which the radio will receive over a given channel or ona given frequency. In some circumstances, the respective hoppingsequences of different radios may be synchronized.

However, radios may hop out of synchronization with neighboring nodesand may even hop according to independent hopping sequences. Forexample, FIG. 3 illustrates that the hopping sequence of RADIO 1 isslightly out of sync with the hopping sequence of RADIO 2. Thus, afrequency hopping system may be employed that does not keep all radiosin-sync as they move through the hopping sequence. Additionally, a firstradio's hopping sequence may be different from a second radio's hoppingsequence. Allowing radios to hop independently may provide advantageswith respect to using the entire spectrum efficiently. A radio may,however, track where each of its neighboring radios are in their ownhopping sequences.

Certain embodiments disclosed herein facilitate the sending of broadcastmessages in frequency hopping networks, advanced metering infrastructure(AMI) systems, and other systems. Various techniques may be used to senda broadcast message quickly and efficiently in a frequency hoppingsystem. In some embodiments, a relatively small packet or “chirp” issent to provide channel and/or time information about a broadcastmessage that will subsequently be sent. These chirps are either targetedat known devices or are sent in a manner to sweep the RF band (i.e., tomany or all of the frequencies used). Devices that hear the chirps willreceive information about the channel and/or time that the actualbroadcast data will be sent. These recipient devices will then listenfor the broadcast data as instructed, e.g., at the specified point intime on the specified channel.

A chirp is a small packet that contains a minimal amount of informationand is considerably smaller than the subsequent broadcast message thatit announces. Sending the chirps first instead of the broadcast messagecan provide various efficiencies. A chirp may be sent to many or all ofthe different frequencies employed by a frequency hopping system. Suchsending can be referred to as sending a “sweep,” i.e., a message thatsweeps most or all frequencies that are used. For example, a device mayreceive a broadcast and send a corresponding chirp on each frequencythat is used on the network. In circumstances in which the chirp issmaller than the subsequent broadcast message, sending the chirps firstto sweep the frequencies and then sending one or a few broadcastmessages (i.e., on fewer of the frequencies) can be more efficient thansending the broadcast message itself on more frequencies. Anotheradvantage of targeting the hopping sequence is that a device is nowtargeting all devices that are out there, which can improve scaling.

In alternative embodiments, chirps can be sent in other ways instead ofsweeping the frequencies. A combination of sweep-based andnon-sweep-based chirp distribution techniques can also be used. Somenodes may send sweep-based chirps and other nodes may send chirps inother ways. For example, some or all nodes can simply send chirps toknown device recipients. If the number of known nodes is close to, orexceeds, the number of channels in the hopping sequence, then it may bebetter to target the hopping sequence with the chirps rather than theindividual nodes. Generally, chirps are send in advance of the broadcastmessages they announce and can be sent in a variety of ways.

One exemplary embodiment provides a method of communicating withmultiple radio devices to inform those radio devices that a broadcastpacket will be sent, so that the radio devices will listen on aspecified channel at a specified time when the broadcast packet is sent.In one embodiment, the chirp is referred to as a rapid fire tickle noacknowledgement (“no ack”) packet and is sent to “n” target devices.Such a chirp may identify the channel that the broadcast packet will betransmitted on and/or the time at which transmission will occur. A chirpis preferably, but not necessarily, made as small as possible tofacilitate sending several chirps in a short time period. For example,the LAN address of the sender may not be important and thus, in somecircumstances, is not included.

Generally, a chirp packet can be as simple as a 1 byte message thatidentifies itself as a chirp packet. Based on this information, arecipient device can retrieve information about a subsequent broadcastmessage. For example, the recipient device may interpret the chirppacket to determine that a broadcast message will occur at a nextinterval of a pre-configured interval and on a particular channel.Alternatively, the chirp packet may provide various other combinationsof information used by recipient devices to facilitate receiving thesubsequent broadcast packet. For example, the chirp may expresslyidentify a particular channel and/or a particular time for the broadcastmessage. Additionally, a chirp may provide information that can be usedto determine whether the broadcast message has already been received bythe chirp recipient.

As shown in FIG. 4, an exemplary chirp packet 400 comprises a packetidentifier 402, a channel identifier 404 specifying on which channel thesubsequent broadcast packet will be transmitted, a time identifier 406specifying the time or time range the subsequent broadcast packet willbe transmitted, and a CRC 408 of other information (e.g., sourceaddress, message ID, fragment number, etc.). If the packet identifier is1 byte, the channel identifier is 1 byte, the time identifier is 1 byte,and the CRC is 2 bytes, and the 5 byte packets are transmitted at 9600baud, each will take about 20 milliseconds. This estimate accounts forthe overhead to get on the channel, ramp up the RF power and put out therequired low level characters to properly identify the message. Thedevice allocates a fixed amount of time for sending the chirps. Aftersending the chirps, the device sends the actual data packet, i.e., thebroadcast message, at an appropriate subsequent time. In one example, adevice spends up to 500 milliseconds sending the chirp packets, which at9600 baud allows up to 25 chirps.

At 9600 baud, it can take about 225 milliseconds to send a 100 bytepacket from one radio to another. In one example, in the time it takesto transmit 3 broadcast packets to specific target devices, the samedevice could send 25 chirps and the actual data packet to a multitude ofdevices. It may have increased its chances 8 times or more over simplysending the packet directly. The number of devices that could actuallyhear the data is limited only by the number of actual devices that canhear the radio's RF signal.

Generally, among other things, a chirp may include information about theslot or channel on which a subsequent broadcast packet will be sent, themaximum time until the subsequent broadcast packet is sent, baud rate,e.g., in 32 millisecond increments, and a packet ID (e.g., as part of aLayer 3 CRC). A hopping sequence slot can be used in place of actualchannel information. For example, a transmitter and receiver can lookthe slot up in their hopping sequence and map it to a physical channel.The packet ID and/or other information such as LAN, Message ID, andFragment IDS may be used for duplicate checking

Following the distribution of chirps, broadcast packets can be sent inaccordance with the information provided by the chirp. In oneembodiment, a broadcast packet may be sent once as a data no ack packetsince a recipient device may have many opportunities to hear a broadcastpacket. Since the device only needs to receive the broadcast packetonce, after the device has heard the broadcast packet, subsequent chirpscan be ignored. A chirp may identify the broadcast packet so that thereceiver can identify if it has already been received. As one example, apacket ID field described above can be used to identify if a packet hasbeen heard before.

Using chirps followed by a broadcast message can provide significantimprovement with respect to the speed and efficiency of distributing abroadcast message. As one example, if the window for sending chirps is480 milliseconds, at 20 milliseconds per chirp and at 9600 baud, 24attempts can be made to send the chirp, followed by roughly 160milliseconds to send the 100 byte broadcast packet as a data no ackpacket. While the success rate would probably not be 100%, a radio couldmake 3 or 4 passes and stop, and the recipient devices could then passthe message on to their own targets. In a relatively dense network,every radio in the network will likely have many opportunities toreceive the broadcast packet. Additional speed and efficiency can beachieved by increasing the baud rate, for example, to 38400 baud orgreater.

In a dense network, steps can be taken to avoid interference. Recipientsmay not be able to hear an actual broadcast packet where there is a highprobability that one of the other devices is sending a chirp packet onthe same channel. These types of issues can be addressed in variousways. For example, data in the chirp message can be used to select asubset of the number of channels in the hopping sequence rather thanforcing all recipients to use a single channel. Only those channels thatare in that subset will be targeted for distributing the message. Inanother example, chirps packets can be transmitted on one set ofchannels and the broadcast packets can be transmitted on a differentset. The physical channels can be divided into four groups. In oneembodiment, two bits from a Layer 3 Message ID field can be used todecide which group of channels to use. This allows the radio to haveequal usage of channels and may facilitate satisfying FederalCommunications Commission (“FCC”) and other requirements. The packet canthen be transmitted on a channel that is, for example, 2 away from thechirp. For example, if the 2 bits of the Message ID are 01, chirps cango out on physical channels: 904.1, 904.5, 904.9, etc., and data packetscan go out on a channel that would be 2 away from this: 904.3, 904.7,905.1, etc. A transmitter may determine what channel a node is currentlyon. If it is on a channel that is in the active group, a chirp is sent.If not, it moves on to the next node. The transmitter may also pick thechannel for the data transmission based on the active group plus 2technique. Generally, to comply with requirements for using channelsevenly over time, something in the broadcast packet that changes can beused to choose channels.

Certain embodiments provide various techniques to determine how and towhom chirps will be sent. For example, if the packet is destined forcollocated radios, then only collocated radios will be targeted. Asanother example, a radio can be flagged to target radios based on noderank, e.g., only radios with Node Rank 0 & 1. As yet another example, aradio can target only nodes on an active node list. If there are manynodes, it may be more efficient to just send to the various frequenciesused in the hopping sequence (i.e., sweep the hopping sequence), ratherthan target individual nodes. Thus, with all of the above examples, ifthe number of potential nodes is greater than the number of channels inthe hopping sequence (or a fixed number as may be appropriate), thenchirps can be sent across the hopping sequence instead of to individualnodes.

After receiving a chirp packet, a recipient radio can keep the chirppacket to check for duplicate messages. This history, in one embodiment,is maintained based on the chirp packet's time to live field, which isthe amount of time that a receiving radio will keep a packet beforediscarding it. In another embodiment, the chirp message history islimited to a maximum number of messages.

FIG. 5 is a flow chart illustrating an exemplary method 500 of using achirp packet to indicate that a broadcast message will be subsequentlysent. Exemplary method 500 involves a first device distributing abroadcast message to a plurality of recipient devices. For example, thefirst device and the recipient devices may be a part of a frequencyhopping network in which nodes of the network communicate based on oneor more frequency hopping sequences and the broadcast message may be amessage that is intended for receipt by all nodes of the network.

The method 500 comprises receiving a broadcast message at a first devicefor distribution to recipient devices, as shown in block 510. The firstdevice may have received the broadcast message in a variety of ways. Inone embodiment, the first device receives the broadcast message byperiodically listening on a channel not specified by the first device'sfrequency hopping sequence. This type of periodic transmitter broadcastmoment distribution technique is described in greater detail below.

The method 500 further comprises sending a chirp packet indicating toany recipient devices receiving the chirp packet that a broadcastmessage will be sent subsequently, as shown in block 520. The chirppacket may identify a channel on which the broadcast message will besent and a time at which the broadcast message will be sent. The chirppacket may also provide information that allows recipient devices toavoid receiving duplicate broadcast messages. For example, it mayprovide a broadcast message identifier that the recipients can use tocompare to determine whether a broadcast message has already beenreceived.

In the case of a frequency hopping network, the first device sends thechirp packet on each channel used on the frequency hopping network. Thistype of sweep can help ensure that many of the potential recipientsbecome aware of the subsequent sending of the broadcast message,regardless of where in a frequency hopping sequence those recipients maybe.

After sending the chirp packet, the method 500 further comprises sendingthe broadcast message, as shown in block 530. In the case of aparticular channel and particular time window, the first device willsend the broadcast packet on the appropriate channel at the appropriatetime. While some embodiments utilize the various chirp and/or channelsweeping techniques described above, other embodiments may additionallyor alternatively use various periodic transmission techniques.

Periodic Transmitter Broadcast Moment

An additional or alternative broadcasting technique particularly usefulin frequency hopping networks involves a periodic transmitter “broadcastmoment,” which is a periodically scheduled break from the use of hoppingsequences. A broadcast moment can be scheduled to interrupt the hoppingsequences so that, at such times, some or all of the nodes are scheduledto be on the same channel for potential broadcasts. Such a periodictransmitter provides a way to send a packet to a large audience quickly.For example, once a second, each node may go to a specified channel andbroadcast if there is a broadcast message to broadcast. The specifiedchannel may change over time so that channels are used evenly. There isa potential cost to this type of technique, since, for example,recipients may stop a current activity every second to listen. This costcan be addressed by broadcasting less frequently. Alternatively or inaddition, this cost can be addressed by configuring the nodes to onlysend and/or listen if the node is not busy. Thus, while using such abroadcast moment may not have a high success rate, it can provide arelatively fast mechanism to send a broadcast to a large group all atonce.

The interval to perform a periodic transmitter broadcast moment can bedetermined to fit the circumstances of the particular system in whichthe technique is used. In a frequency hopping system generally, sinceevery device in the network must stop and listen at times based on theinterval length, the shorter the interval, the more time all radios areoff channel and not available for normal communication. In addition, theperiodic transmitter may put excessive RF noise into the system. If thebroadcast transmitter transmits a packet on every broadcast cycle, thenthat noise has to be factored in as extra load on the system.

Periodic broadcast transmission may be appropriate in variouscircumstances. For example, some devices may communicate with thousandsof other devices (e.g., routers), many of which may be able to hear butnot transmit back. A system can be configured so that each broadcastpacket gets a fixed number of chances, e.g., five chances, to bebroadcasted before it is discarded. For example, a packet “mood” whichhas no value during a broadcast, can be used to specify how manyattempts a periodic transmitter should make for the packet.Periodically, e.g., every 2 hours, the transmitter may put a maintenancepacket on the broadcast queue to be transmitted. This can be used toallow the receivers to refresh their delta tick, among other things. Ifa radio is in the middle of receiving or transmitting a packet, thedevice can miss the broadcast. For a receiver, this should beinsignificant since it may have multiple chances to receive the message.Similarly, for transmitters, this is not an issue as long as they do notmiss several in a row.

The interval of the broadcast cycle may be determined to allow anappropriate amount of broadcast listen time. In one exemplary system, a5 second interval requires that every radio that is listening will haveto stop once every 7 channels of their hopping sequence and listen for75 milliseconds for each interval. In this example, this amounts toabout 1.5% of its time. However, if required to listen to everybroadcast moment, a radio may have to set aside additional receive timeto guarantee that it is not busy when the broadcast moment arrives.Thus, to ensure that an interval is not missed, regular activity may bestopped for a greater percentage of the device's time, which may beunacceptable for some purposes. For example, listening for extendedintervals at every broadcast moment could amount in more than 10% of adevice's regular receive time being lost. If a radio is not required tolisten to every transmit, however, the radio is tied up for a smallertime intervals and only used from such messages when the device is nottied up with regular activity.

A receiving device may start receiving a fixed amount of time, e.g., 25milliseconds, before the expected broadcast time to account forpotential drift. Similarly, time, e.g., another 25 milliseconds, can beadded to give any incoming packet time to start receiving. Once thistime is up, the receiver will continue to receive only if a packetcontinues to be received. Once the receiver goes idle, the receiverreturns to its normal hopping sequence.

In a periodic broadcast system, the transmitters may need to tell theother radios when and where the next transmission may occur. Devicesthat are set up to transmit may include this information, for example,in their acquisition sync packets and a few other key packets. Thus,when a device first boots up, if it acquires a periodic transmitter, thedevice gets that information right away.

In one exemplary embodiment, a 2-byte value indicates where in thetransmitter's hopping sequence the next transmit will occur. This valuecan be in, as an example, 4 millisecond increments. If the receiver istracking the other radio's delta tick, this value does not need to berefreshed, provided the receiver keeps moving it forward with eachtransmit interval. A 2-byte value can be used to indicate the intervalbetween transmissions and can also be in 4 millisecond increments. Thisinformation is tacked onto the end of an acquisition sync, for example,using Layer 2 tag functionality. The data should be in the acquisitionsync packet. In one example, to make it easy for the receivers to giveup on a radio if they no longer can hear packets from it, the receiversare set up to dump a broadcast transmitter in favor of another one ifthey have not heard an acquisition sync in a given amount of time, e.g.,in the last 24 hours. A receiver can latch onto the best transmitters,for example, based on received signal strength indication (“RSSI”).

Moreover, a periodic transmitter broadcast moment technique can be usedwith the various chirp and/or channel sweeping techniques describedabove. For example, a periodic transmitter broadcast moment techniquecan be used to distribute a broadcast message to a large percentage(e.g., 50%) of the potential recipients and then each of thoserecipients can further distribute that message using the chirp and/orchannel sweeping techniques. In a network, nodes can be configured withmultiple broadcast message distribution algorithms. For example, a givennode may be configured to send broadcast messages using either a chirpthen broadcast message technique or a periodic transmitter technique. Ina network, such as an AMI system, the routing infrastructure can beconfigured to use the periodic transmitter techniques and the meternodes can be configured to use the chirp then broadcast techniques.Various combinations of techniques can be used, including combinationsinvolving different techniques than are described herein. Generally, alldistribution techniques provide some advantages and disadvantages. Thoseadvantages and disadvantages, as well as considerations with respect tohow much transmission/message success is required, can be used to selectan appropriate combination of one or more distribution techniques.

General

The foregoing description of the embodiments of the invention has beenpresented only for the purpose of illustration and description and isnot intended to be exhaustive or to limit the invention to the preciseforms disclosed. The techniques of the invention are not limited to AMIsystems, mesh networks, or any other particular network configuration.Thus, in general numerous modifications and adaptations are apparent tothose skilled in the art without departing from the spirit and scope ofthe invention.

That which is claimed:
 1. A system comprising: a mesh network comprisinga plurality of devices configured to communicate using one or morefrequency hopping sequences; a first device of the plurality of devicesconfigured to store and send a broadcast message at a time and on afirst channel that is periodically-scheduled; and a second device of theplurality of devices, wherein the second device receives the broadcastmessage by listening at the time on the channel that isperiodically-scheduled.
 2. The system of claim 1 wherein some of theplurality of devices receive a broadcast message by periodicallystopping a frequency hopping sequence and listening on another channel,wherein at least some of the plurality of devices then send chirppackets on multiple frequencies indicating to any recipient devices thatthe broadcast message will be sent subsequently.
 3. The system of claim2 wherein the chirp packets identify on which channels the broadcastmessage will be sent, at what times the broadcast message will be sent,and provide information that allows recipient devices to avoid receivingduplicate broadcast messages.
 4. The system of claim 1 wherein the firstdevice's frequency hopping sequence is the same as the second device'sfrequency hopping sequence.
 5. The system of claim 1 wherein the firstdevice's frequency hopping sequence is different than the seconddevice's frequency hopping sequence.